<!DOCTYPE html>
<html lang="zh">
<head>
  <meta charset="UTF-8">
  <title>外部样式表</title>
  <!-- 在link元素中链接样式表 -->
  <link rel="stylesheet" href="external.css" type="text/css">
  <style rel="stylesheet" type="text/css">
    /* 在style标签中使用import关键字导入样式表 */
    @import url(external.css);
  </style>
</head>
<body>
外部样式表，指在网页中通过link元素的href属性引入外部样式文件定义元素的样式<br>
<iframe src="introduction.html" width="65%" height="200px">你的浏览器不支持框架</iframe>
<p id="p1">段落</p>
<p id="p2">段落</p>
<pre>
  预排版
  <b>提醒注意</b>
  预排版
</pre>
<div>
  <strong>强调</strong>
</div>
<table id="table1">
  <tr class="tr1">
    <td id="td1">单元格1</td>
    <td id="td2">单元格2</td>
    <td id="td3">单元格3</td>
  </tr>
  <tr class="tr2">
    <td id="td4">单元格4</td>
    <td class="set1" id="td5">单元格5</td>
    <td id="td6">单元格6</td>
  </tr>
  <tr class="tr3">
    <td id="td7">单元格7</td>
    <td id="td8">单元格8</td>
    <td id="td9">单元格9</td>
  </tr>
</table>
<table id="table2" border="1" width="220">
  <tr class="tra">
    <td class="set1">单元格a</td>
    <td class="set1">单元格b</td>
  </tr>
  <tr class="trb">
    <td class="set2">单元格c</td>
    <td class="set2">单元格d</td>
  </tr>
</table>
</body>
</html>